Bulletin of the Chemical Society of Japan
Online ISSN : 1348-0634
Print ISSN : 0009-2673
ISSN-L : 0009-2673
Racemization Reactions of Cobalt(III) Complexes of Ethylenediaminetetraacetate and Trimethylenediaminetetraacetate
Hiroshi OginoMasatake TakahashiNobuyuki Tanaka
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1973 Volume 46 Issue 1 Pages 178-183

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Abstract

The kinetics of racemization reactions of ethylenediaminetetraacetatocobaltate(III), CoIIIedta, and trimethylenediaminetetraacetatocobaltate(III), CoIIItrdta, were investigated in acid solutions. The rate law for the racemization of (+)546CoIIIedta is:
\fracd[(+)546CoIIIedta]dt=−2\frackr1Ka+kr2[H+]Ka+[H+][(+)546CoIIIedta]
where Ka is the equilibrium constant of the reaction:
(+)546CoIII(H2O)Hedta\ ightleftarrows(+)546CoIIIedta+H+
The values of kr1 and kr2 at 120°C and at an ionic strength of 0.53 are 2.0×10−5 sec−1 and 5.6×10−4 sec−1 respectively. The rate law for the racemization of (+)589CoIIItrdta is:
\fracd[(+)589CoIIItrdta]dt=−2kr2[H+][(+)589CoIIItrdta]
The value of kr2 at 120°C and at an ionic strength of 0.53 is 1.9×10−5 l mol−1 sec−1. It is known that the rate of the racemization reaction of optically-active CoIIedta2− is accelerated by the presence of CoIIedta2− because of the electron-exchange reaction between these two species. In this paper, the electron-exchange reaction between CoIIItrdta and CoIItrdta2− is also investigated by the utilization of the optical activity. This reaction proceeds faster than the reaction between CoIIIedta and CoIIedta2−.

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